Electrically tunable notch filters

Abstract

This invention provides a notch filter including a main transmission line, a coupling mechanism, and at least one electrically tunable resonator coupled to the transmission line through the coupling mechanism. A tunable dielectric varactor or a microelectromechanical variable capacitor is provided in each of the resonators. Wireless telephone handsets that include the filter are also included.

1 . A wireless telephone handset comprising: 
 an antenna connection;    a diplexer coupled to the antenna connection;    a transmit section connected to a first port of the diplexer;    a receive section connected to a second port of the diplexer; and    wherein the diplexer includes first and second notch filters, each of the notch filters comprising a main transmission line, a first coupling mechanism, and a first electrically tunable resonator coupled to the main transmission line through the first coupling mechanism.    
     
     
         2 . A wireless telephone handset according to  claim 1 , wherein each of the first electrically tunable resonators includes a first tunable dielectric varactor or a first microelectromechanical variable capacitor.  
     
     
         3 . A wireless telephone handset according to  claim 2 , wherein the first tunable varactor comprises: 
 a substrate having a first dielectric constant and having a generally planar surface;    a tunable dielectric layer positioned on the generally planar surface of the substrate, the tunable dielectric layer having a second dielectric constant greater than said first dielectric constant; and    first and second electrodes positioned on a surface of the tunable dielectric layer opposite the generally planar surface of the substrate, said first and second electrodes being separated to form a gap therebetween.    
     
     
         4 . A wireless telephone handset according to  claim 1 , wherein the first coupling mechanism comprises one of: 
 a first capacitive probe, a first inductive loop, a first iris window, a first evanescent waveguide piece, a first slot, and a first hole.    
     
     
         5 . A wireless telephone handset according to  claim 1 , wherein the main transmission line comprises one of: 
 a coaxial transmission line, a microstrip line, a stripline line, a rectangular waveguide, a coplanar waveguide, and a ridged waveguide.    
     
     
         6 . A wireless telephone handset according to  claim 1 , wherein each of the first and second notch filters further includes: 
 a second coupling mechanism; and    a second electrically tunable resonator coupled to the main transmission line through the second coupling mechanism, wherein the first and second coupling mechanisms are spaced ¼ wavelength apart at an operating frequency of the filter.    
     
     
         7 . A wireless telephone handset comprising: 
 an antenna connection;    a diplexer coupled to the antenna connection;    a transmit section connected to a first port of the diplexer;    a receive section connected to a second port of the diplexer; and    wherein the diplexer includes first and second notch filters, each of the notch filters comprising a bandpass filter connected between a termination and one of a circulator or a 3 dB hybrid.